1. Field of the Invention
The present invention relates to a video data distribution system and method, and more particularly to a system and method for distributing video information to a plurality of client data terminals over a network.
2. Description of the Related Art
Remote video monitoring systems have been used to continuously watch one or more objects of interest for certain purposes, e.g., to protect environments or to detect a sign of natural disasters. Typically, dedicated central monitoring facilities equipped with multiple video monitor units are provided to enable centralized monitoring of target objects under observation.
On the other hand, there are such demands that video images of remote objects be accessed through a network from locations other than the dedicated central facilities. This is motivated by the recent advancement of high-performance personal computers (PCs), which has made it possible for general users to enjoy high-speed computing (including video processing) with extremely powerful CPUs and rich memory resources. An increasingly large number of PCs are used today, many of which are linked to each other as Intranet or local area network (LAN) clients. Such a PC network may serve as a suitable infrastructure for sharing remote video information by many users. With appropriate video distribution capabilities implemented on LAN environments, it would be possible for PC users to conveniently make access to remote object images at any time, without using dedicated monitoring facilities.
However, most existing LANs are not suitable for the above-described usage because they are designed basically to transfer computer programs and data files, rather than to convey multimedia traffic which requires much wider bandwidths. In addition, the existing PCs vary greatly in processing power, depending on the date of their deployment.
To deliver video information over a LAN, conventional transmission systems use point to point connections established between a video server and a plurality of client PCs. Intraframe coding algorithms such as Motion JPEG are mainly employed in those conventional systems, along with simple frame subsampling techniques to reduce bitrates. These conventional video transmission techniques, however, have several drawbacks as described below.
First, conventional techniques use connection-oriented communication services, the performance of which depends on total message traffic on the LAN being used. For this reason, only a limited number of client PCs can make simultaneous access to the video source.
Another drawback is that intraframe coding provides too low video compression ratios. In a network environment with a limited transmission bandwidth, insufficient compression would cause unnatural visual effects on the reproduced video, particularly in such a scene that includes rapid motions. Because of this drawback, the conventional systems may not be able to satisfy the user requirements concerning picture quality.
Still another problem with the conventional systems may become apparent in such a situation where both high-performance PCs and low-performance PCs coexist on a single LAN environment. High-performance PCs can decode and display video pictures at a high frame rate, taking advantage of their powerful CPUs, whereas low-performance PCs can only do the same job at limited rates because of their less-capable CPUs. If a high rate video bitstream is broadcast to such non-uniform clients over the network, the low-performance PCs would only be able to reproduce poor video images, or in extreme cases, they would yield nothing. Broadcasting a low rate video bitstream, on the other hand, may not disrupt the decoding operation of low-performance PCs. However, this certainly shuts the high-performance PCs out of the chance to demonstrate their advantages.
In addition to indifference toward the above-described heterogeneity of PC clients in terms of video processing performance, the conventional video broadcasting techniques fail to provide effective measures to deal with transmission errors, which a client PC may encounter during the reception of a coded video stream.